The interface between two immiscible electrolyte solutions (ITIES) can act as a scaffold for the assembly of nanometer-sized objects. Here we followed the adsorption of silica nanoparticles of 12 nm diameter at the ITIES by AC voltammetry and their interactions with methylene blue (MB+), selected as a model ion, by cyclic voltammetry and UV-vis absorption spectroscopy. We determined the association constant, K-ads(aq), of adsorption of MB+ onto silica nanoparticles to be 1.66 10(5), which indicated a strong affinity between them. This strong affinity shifted the Gibbs free energy of transfer by -8.9 kJ mol(-1). This is in contrast with the other two ions investigated (Eosin B and tetraethylammonium), which demonstrated low affinity for the silica nanoparticles. By combining the ability of silica to adsorb onto the ITIES and their affinity for MB thorn, we were able to accumulate MB+ at the ITIES. (C) 2018 Elsevier Ltd. All rights reserved.